This invention relates generally to gas turbine engine exhaust nozzles and more particularly, to methods and apparatus for reducing turbine engine exhaust nozzle basesheet stresses.
At least some known gas turbine engines include an exhaust nozzle including a variable geometry system. The variable geometry system adjusts an area of the exhaust nozzle through the use of flaps and seals. The flaps define discrete sectors of the flowpath, and the seals form the remaining flowpath between adjacent flaps. Because the exhaust nozzles are subjected to high temperatures and thermal gradients as a result of hot combustion gases exiting the engine, the variable geometry systems must maintain a coherent flowpath while shielding the structural components of the variable geometry system.
At least some known flap systems consist of a backbone and a basesheet. The backbone secures the basesheet within the variable geometry system. To facilitate extending a useful life at high temperature operation, at least some known basesheets are fabricated from non-metallic materials, such as ceramic matrix composite (CMC) materials.
At least some known basesheets are divergent and are attached to the backbone using mechanical fasteners, such as rivets or bolts. Over time, continued thermal expansion may create local stress concentrations within the divergent basesheets. Furthermore, continued thermal cycling may cause the divergent basesheet to deform or distort. Because such tensile strength may be a weakest load path through the basesheet, continued thermal cycling may cause premature failure of the basesheet.